Teeth become discolored with age, blood, amalgam restorations, antibiotics such as tetracycline, and substances in food, beverages, tobacco and salivary fluid. Tooth structures which are responsible for a stained appearance are enamel, dentin, and the acquired pellicle.
Tooth enamel is predominately formed from an inorganic substance, hydroxyapatite crystals, along with approximately 5% organic materials, predominantly collagen. The dentin is composed of about 20% protein including collagen; the balance of inorganic materials including hydroxyapatite crystals. The acquired pellicle is a proteinaceous layer on the surface of tooth enamel, and that may be removed after an intensive tooth cleaning.
Tooth stains are generally classified as either extrinsic or intrinsic, depending on whether the stain is on the surface of the tooth within the acquired pellicle or within the tooth structure itself within the enamel or dentin. For example, extrinsic staining of the acquired pellicle can occur from foods or compounds, which contain tannins and other polyphenolic compounds which become trapped in the lightly bound proteinaceous layer on the surfaces of the teeth.
Intrinsic staining, on the other hand, occurs when chromogens and pre-chromogens penetrate the enamel and dentin and become tightly bound to the tooth structure. Intrinsic staining can occur when blood or amalgam products leach into the enamel and dentin. Intrinsic staining likewise can occur systemically from excess fluoride intake during enamel development leading to a mottled yellow or brown stain of fluoresce staining. Intrinsic staining is not removable by mechanical methods of tooth cleaning and generally requires the use of chemicals, for example strong oxidizing agents such as hydrogen peroxide which can penetrate into the tooth structure to effect a change in the light absorbtivity of the stain chromogen and/or the solubility of the chromogens.
The desire for whiter, lighter teeth is considered to be cosmetic and desirable in today's cosmetically-orientated society. Tooth bleaching is generally accomplished by gels, pastes, or liquids which contain an oxidizing agent such as hydrogen peroxide that attack (i.e., chemically react with) the chromogen molecules, making them colorless and/or water soluble, making the tooth appear lighter and brighter, thus resulting in lighter brighter teeth.
The most commonly used oxidizing agent is hydrogen peroxide (H2O2), such as from carbamide peroxide, which is mixed with an anhydrous viscous carrier containing glycerin and/or propylene glycol and/or polyethylene glycol. When in contact with water, carbamide peroxide dissociates into urea and hydrogen peroxide. The hydrogen peroxide in the presence of water then disassociates into water and a nascent oxygen anion species. It is these highly-nascent oxygen species, which react with the stain making them more water soluble, transparent, or both.
There are several known delivery systems to deliver carbamide peroxide to the surfaces of the teeth.
A common approach is to have a dental professional construct a custom-made tray from an impression of the patient's teeth. The oxidizing gel is dispensed into the tray by the patient and the tray is worn over the teeth intermittently for a period of two weeks to several months, depending on the severity of the staining. This approach can cause tooth sensitivity in over 50% of the patients, and it can be uncomfortable for the patients to wear the tooth bleaching trays. Tooth sensitivity is believed to result from the movement of fluid through the dentinal tubules, which is sensed by nerve endings within the tooth. The carriers, glycerin propylene glycol and polyethylene glycol, draw fluids toward them and therefore contribute to the tooth sensitivity often experienced by wearing a bleaching tray.
Another approach is to incorporate the oxidizing agent in a strip and have the patient wear the strip intermittently over a period of two weeks. This approach also has the disadvantage of being awkward for patients to wear, and many patients wearing the strips, also experience tooth sensitivity. Further, the strips have an inherent problem of contacting the teeth only on the facial surfaces and most of the staining occurs in between the teeth in the interproximal areas where in can be difficult to place the strip, having it in contact with the tooth.
Another recent approach is to simply paint on the oxidizing agent, carbamide peroxide or hydrogen peroxide, directly on the teeth. In products, which are gels containing glycerin and/or propylene glycol or polyethylene glycol, tooth sensitivity can be experienced, and the gels can easily be removed by the lips and tongue, thereby decreasing their effectiveness.
One approach involves dissolving carbamide peroxide in alcohol, and a resin. The resultant compound is applied directly onto the teeth, and the alcohol evaporates, leaving a sticky resin film or precipitate remaining on the surface, of the teeth. When saliva contacts the teeth, the peroxide is released in a relatively strong concentration for a period of up to 20 minutes. This product contains no glycerin, propylene glycol, or polyethylene glycol and tooth sensitivity is lessened with some resultant whitening. These products take approximately two weeks of use several times a day to achieve a desired result.
To address the problem of taking excessive time to whiten teeth, manufacturers developed systems used by a dentist and only available in a dental office (with and without a light source), to whiten teeth in approximately one hour. These systems generally use oxidizing compositions (hydrogen peroxide up to 35%), which are applied directly on the surfaces of the teeth in a dental office under the supervision of a dentist or dental hygienist. Owing to the high concentration of oxidizing agents contained in these in-office products, they can be hazardous to the patient if not handled carefully. The patient's soft tissues—gingiva, lips and tissues—must be isolated from potential exposure to a concentration of oxidizing agent by the use of a rubber dam or by covering the soft tissues with a polymerizable resin that is shaped to conform to the gingival contours and subsequently cured by a high intensity light source operable only by a dentist. These dentist in-office whitening systems are expensive to the patient.
Known patents directed to these various tooth whitening systems include:
U.S. Pat. No. 4,952,143 to Becker et al.; and
U.S. Pat. No. 5,032,178 to Cornell.
These known systems have drawbacks.
A commercial product, called Opalescence, from Attica Dental Products, Inc., South Jordan, Utah is known.
Further known systems are set forth in:
U.S. Pat. No. 5,785,527 to Jensen et al.; and
U.S. Pat. No. 6,517,350 to Diasti et al.
One commercially available illuminating system is from Union Broach, a Health/Claim Company, New York, N.Y.
Other known United States patent documents include:
U.S. Pat. No. 4,450,139 Bussiere et al.;
U.S. Pat. No. 5,457,611 Verderber;
U.S. Pat. No. 6,331,111 Cao;
U.S. Pat. No. 6,343,933 Montgomery;
U.S. Pat. No. 6,416,319 Cipolla;
U.S. Pub. No. 2003/0017435 Ibsen et al.;
U.S. Pub. No. 2003/0036037 Zavitsanos et al.; and
U.S. Pat. No. 4,661,070 to Friedman.
There is a need for improved compositions and devices for whitening teeth that are capable of whitening the teeth rapidly and inexpensively by consumers without damaging the tooth enamel, dentin, or the pulp, and that are able to be used at a lower concentration of peroxide, thus enabling the patient to use the product at home without harming the tissues, or causing tissue irritation, or causing tooth sensitivity.